The present invention generally relates to a battery disconnection detecting apparatus, particularly to a battery disconnection detecting apparatus for use in a vehicle which has storage devices or semiconductor memories to store and hold data with electric power supplied thereto from a battery.
A conventional electronic control unit (ECU) for an engine of a vehicle, for example, is so designed as to learn various control constants for suitably controlling the engine based on the learned control constants when the engine is in operation after an ignition switch (IG switch) is turned ON. These learned control constants are updated and stored in a random access memory (RAM) whenever necessary when the engine is in operation. The RAM is composed of a nonvolatile memory which holds the stored control constants as long as electric power is supplied thereto from a battery. In this arrangement, even when the IG switch is turned OFF and the engine is stopped, the newest learned control constants computed most lately is continuously held in the RAM. Accordingly, when the IG switch is turned ON again and the engine is restarted, the engine can be controlled based on the newest leaned control constants computed during the previous operation of the engine. In this way, by reflecting the newest learned control constants computed during the previous operation of the engine in the control of the engine started next time, the engine can be controlled always suitably.
For an electric power circuit for vehicles, one example has been disclosed in the Japanese Examined Utility Model Publication No. 3-33566, for instance. In this prior art, to a central processing unit (CPU) is connected to a battery through an IG switch, so that electric power is supplied from a battery to the CPU when the IG switch is turned ON. On the other hand, a RAM for storing data including learned control constants is continuously supplied with electric power from the battery through an electric power supply route which is different from an electric power supply route to the CPU. In this prior art, however, even when the electric power supply route from the battery to the RAM is disconnected and the electric power supply to the RAM is interrupted, it is so arranged that, when the IG switch is turned ON, the electric power from the battery is supplied through a backup circuit to the RAM. According to the above prior art, therefore, even when the above disconnection is caused when the IG switch is turned ON, not only the CPU but also the RAM are supplied with electric power from the battery. As a result, the CPU judges that the RAM is in normal operation, and starts controlling the engine based on the data stored in the RAM.
According to the prior art disclosed in the above publication, even when the electric power supply route from the battery to the RAM is disconnected, when the IG switch is turned ON, the RAM is supplied with electric power. However, when the IG switch is turned OFF, electric power supply to the RAM is interrupted, and the data stored in the RAM is lost or destroyed. In this prior art, therefore, when the IG switch is turned ON again and the engine is restarted, the engine is controlled based not on the newest learned control constants computed during the previous operation of the engine but on the learned control constants destroyed by the interruption of the electric power supply. Therefore, a problem with the prior art in the event of the above disconnecting is that the newest learned control constants computed during the previous operation of the engine can not be reflected in controlling the engine when the engine is started next time, and therefore, the engine can not suitably be controlled particularly at the time when the engine is just started again.
When the interruption of the electric power supply is temporarily caused by the temporary removal of the battery for replacement, or the like, the engine can not properly be controlled only when the engine is started next time, which may not pose any serious problem. However, when the interruption of the electric power supply is continuously caused by the disconnection of the electric power line, the engine can not suitably be controlled whenever the engine is started, which may pose serious problems such as the degradation of exhaust emission whenever the engine is started again.
To solve the above problem, it is considered that an EEP-ROM could be used as a memory for storing such data as the learned control constants. The EEP-ROM can electrically write and erase data, and also can hold the stored data even when the electric power supply is interrupted. However, as the commercially available EEP-ROM can rewrite the data only for the limited number of times, a problem with this EEP-ROM is that it is not appropriate to apply the EEP-ROM as a memory to a case where the learned control constants therein are subjected to frequent rewriting.